1. Field of the Invention
The present invention relates to a camera having an autofocus system with the capability of searching an in-focus position of a focusing lens group while moving the focusing lens group.
2. Description of the Prior Art
A contrast detection (contrast measurement) autofocus system which measures contrast to detect the maximum contrast (or peak contrast) is generally used as an autofocus (AF) system for compact digital cameras. Additionally, a contrast/phase-difference based hybrid autofocus system has been developed (refer to Japanese Laid-Open Patent Publication (Kokai) 2004-309867). According to a conventional contrast detection method, an image capturing operation is repeated to capture images at different lens positions of a focusing lens group while the focusing lens group is driven stepwise between the near side (near extremity) and the far side (far extremity) thereof, a peak contrast value is determined by detecting contrast values of the captured images, and the focusing lens group is moved to a lens position thereof at which the peak contrast value is obtained. Alternatively, a phase-difference method is for determining an in-focus position from a phase difference between divided object images.
In the case of an AF system according the conventional contrast detection method, it is sometimes the case that the camera is focused on a non-target object positioned in front of (on the near side) or behind (on the far side) a target object so as to be focused on the non-target object after the completion of an AF operation. In this case, the photographer will again depress the release button by half a step so that the AF operation is performed again. Nevertheless, in each of the conventional contrast detection autofocus system and the conventional phase-difference autofocus system, it is difficult for the photographer to bring a target object into focus because the focusing lens group is again driven stepwise over the entire range of movement thereof, from the near extremity to the far extremity.
In the aforementioned Japanese Laid-Open Patent Publication 2004-309867, the searching range according to a contrast detection method is limited in accordance with the result of measurement of an AF operation according to a phase-difference method. However, since the searching range is limited to a range having based on (centered about) the lens position of the focusing lens group which is obtained by the phase-difference method, an object detected by the phase-difference method can be brought into focus more precisely; however, an object positioned in front of or behind such an object detected by the phase-difference method cannot be brought into focus.